core

## Constructing a Width Feature

You can construct a Width feature from two opposing sides of a notch, tab, or other similar surfaces. The Width feature is useful to the GD&T standard which requires the width as a Datum in Feature Control Frame dimensions. For more information on Feature Control Frame dimensions, see "Using Feature Control Frames".

Construct Width dialog box

Width constructions require two input features, one feature for each opposing side of the notch or tab.

PC-DMIS supports the following two Width constructions:

- 2D - This is constructed between two opposing lines.

- 3D - This is constructed between two opposing planes.

Width is considered an outer (OUT) feature when the planes or lines come from a tab-like geometric feature. It is considered an inner (IN) feature when the planes or lines are measured from a notch-like geometric feature.

The vector of the Width feature points from the first selected feature perpendicular to the second feature.

To construct a Width feature:

1. Measure the required two features (two lines or two planes) on the opposing sides of a notch, tab, or other two opposing surfaces. These are the two features you will use when constructing the width.

2. Open the Construct Width dialog box in one of these two ways:

- Select Insert | Feature | Constructed | Width.

- From the Construction toolbar, click the Width button.

3. Select 2D or 3D.

- If your input features are two lines, select 2D. The feature list only shows lines.

- If your input features are two planes, select 3D. The feature list only shows planes.

4. From the feature list, select the two input features for the construction.

5. Select In or Out:

- If the Width feature contains material between the two opposing sides, like a tab, it's an outer feature. Select Out.

- If the Width feature does not contain material between the two opposing sides (like a notch), it's an inner feature. Select In.

6. From the fitting list, select the type of fitting algorithm to use: Best Fit or Best Fit Recomp.

7. From the math algorithm list, select the Best Fit math algorithm to use. The available options are:

- Maximum Inscribed (MAX_INSC)

- Minimum Inscribed (MIN_INSC)

- Least Square (LEAST_SQR)

For more information, see "Best Fit Type" under "Constructing a Best Fit or Best Fit Recompensate Circle".

8. If you want to define the theoretical Width information, mark Specify theos and then type the theoretical centroid in X,Y, and Z boxes; type the theoretical vector in the I, J, and K boxes; and then type the width between the two sides in the Width box.

9. Click Create to insert the Width feature into the measurement routine.

The Edit window command line for the width construction shows:

feature_name=FEAT/WIDTH,TOG1,TOG2,TOG3,TOG4
THEO/<x_cord,y_cord,z_cord,i_vec,j_vec,k_vec>,length
ACTL/<x_cord,y_cord,z_cord,i_vec,j_vec,k_vec>,length
CONSTR/TOG5,TOG6,feat1,feat2

TOG1= CARTESIAN or POLAR.

TOG2= IN or OUT. This is for display only; you cannot use the Edit window to edit this.

TOG3 = MAX_INSC / LEAST_SQR / MIN_CIRCSC

TOG4 = YES or NO. These are user-defined theoretical values.

TOG5 = The constructed feature type.

TOG6 = BEST FIT / BEST FIT RECOMP

Notes

You can use a 2D Width feature as secondary and tertiary datums in alignments, but you can use a 3D Width as primary, secondary, and tertiary datums.

If you create a Location dimension of the constructed Width feature, the X, Y and Z axes represent the midpoint of the Width feature. The L axis represents the length of the Width feature.

To calculate a Minimum Circumscribed or Maximum Inscribed Width feature, the hit locations on the two opposing features must have a sufficient amount of overlap.

If d is the overlap distance and w is the width distance (as shown in the figure below), the recommended ratio should be:

d/w = 1 or more

If an overlap is not feasible due to the physical structure of the part, you must use the Least Square method for the Width calculation instead.

For example, in this top-down view of a part, d represents the amount of distance between the two sets of hits where overlap occurs on the two sides, and w represents the Width feature's distance between the two sides. Suppose d = 1.5 and w = 3. The ratio of d/w is .5. The recommended ratio is 1. So, there may not be enough overlap for the Minimum Circumscribed or Maximum Inscribed fitting algorithms. In such a case, use the Least Squares algorithm instead: